The use of hematological analysis as a clinical tool for the recognition and treatment of various diseases has become more widespread due to the availability of automated instrumentation capable of economically performing this analysis. Since pathological changes can often be detected in the distributions of various blood cell subpopulations, hematological analyses can be used to detect diseases as well as to monitor therapies directed at the various diseases.
The relationship between the various hematological analyses and the particular application each variable has to malignant disease is described by Dr. David Bessman, MD, in "New Hematologic Indices: Use in Management of Malignant Diseases," Tex.Med. 80:33-35, 1984. For example, improved anemia classification is made possible by analyses of hemoglobin content, mean corpuscular volume(MCV) and red cell distribution width(RDW).
Leukocyte differentiation is also valuable in the detection of diseases and monitoring therapeutic effects. One valuable use, also reported in Dr. Bessman's article, is in outpatient chemotherapy, where drug administration depends in part on neutrophil and total white cell count. The differential may also be used to detect rare abnormalities, such as myelocytes or occasional blasts. A discussion of the unique problems associated with differentiating white cell subpopulations is presented in the detailed description of the invention below.
Comparisons have also been made between manually performed microscopic blood count determinations, and automated instrumentation for hematalogical analysis which mimics the visual smear technique. The results of these comparisons are compiled in Dutcher, Dr. Thomas F., "Automated Leukocyte Differentials: A Review and Prospectus," Lab. Med. 14: 483-487, 1983. Briefly, it has been reported: (1) The instruments are equal to or better than technologists with regard to precision (repeatability on the same specimen or same blood smear), especially in the classification of bands and monocytes. (2) The instruments are equal to or better than technologists with regard to accuracy, at least relative to finding abnormal cells (accuracy, as thought of in chemistry or even cell counting, is nearly impossible to assess in differential counting because of the inherent variability in 100- or 200-cell differentials). (3) The instruments produce results faster than technologists as timed from presentation of the slide to results available for reporting. (4) The instruments segregate smears into normal or abnormal (abnormal because of cell distribution outside normal range and the presence of abnormal cell types) as well as do technologists. The three part white cell differential instrumentation of the instant invention does not possess the same drawbacks as the instrumentation discussed in Dr. Dutcher's article. The reagents and cell size resistivity measurements of the present instrumentation provide greater accuracy than available in other automated instruments. This improvement in accuracy and levels of detectability, however, enhances the conclusions reached by Dr. Dutcher.
One of the most important criteria with respect to the purchase of such instrumentation has been cost. Dr. Dutcher's article reports that it is generally agreed that a daily workload of 250 to 300 or more differentials is required to justify the purchase on purely financial grounds. Although this number may vary somewhat for three-part differential instrumentation, it provides an order-of-magnitude estimate of the required throughput. Obviously, such a workload is atypical of a private practitioner's daily patient load. Consequently, hematological instrumentation has not become a standard of the private practitioner, but instead has been reserved for the clinical setting in which such workload threshholds can more easily be met. This invention, for the first time, makes economically possible the use of hematological instrumentation in the private practice without undue financial burdens on the practitioner or his/her patients. Previous investigators have discussed the need for providing a well-controlled lysing reaction, since white cell subpopulation enumeration and distribution is a complex function of cell lyse rates. It is reported, e.g., that accurate data can only be obtained if the lysing reagent addition step and transducer measurement step are precisely timed. See C. J. Cox et al., "Evaluation of Coulter Counter.RTM. S Plus IV" A.G.C.P. p.297, Sept., 1985. With this paramount design criterion in mind, it has been a common belief that white cell differentiation can only be accomplished on a fully automated instrument. Only in this manner can the precise timing required for this sensitive analysis be met. This invention recognizes, for the first time, that the timing of the dilution step is not as critical as the timing of the lysing reaction step and, therefore, the timing of this step does not have to be as precisely controlled. In this invention, once the dilution has been made off-line, either manually or semi-automatically, the diluted sample can be presented to the automatic instrument which introduces a carefully controlled volume of the lysing reagent at a precise rate and then measures and counts cell size. This modification of the dilution step, while reducing the complexity of the instrumentation, results in substantial savings in initial instrument costs, thereby making this semi-automatic hematological analyzer available to the office practitioner at a reasonable level of investment.
As discussed above, the use of platelet and red and white blood cell population distributions, and other physical characteristics of the various cells, to detect diseases at very early stages, or to monitor therapies for cancer and other disorders, greatly improves chances for satisfactory patient outcome. Making a hematological instrument available to the practitioner for use in his/her office places this line of detection at even earlier stages of patient screening. Thus, preventative measures can be taken more quickly and more effectively to treat detected diseases. The use of such instruments in the practitioner's office also makes the monitoring of chemotherapy much more convenient for the patient, minimizing the distances, expenses and waiting involved in the clinical setting.
Therefore, it is an object of this invention to provide a method for use with a low cost instrument for performing platelet and red and white blood cell analyses.
It is a further object of this invention to provide a method for use with an instrument which is capable of accurate platelet and red and white blood cell analyses and which is economically available for practitioners' use in the setting of their office.
It is still a further object of this invention to provide a method for use with instrumentation which will increase the availability of the valuable information derived from hematological data.